title: An amino-terminal signal sequence abrogates the intrinsic membrane-targeting information of mitochondrial uncoupling protein.
abstract: Mitochondrial uncoupling protein, a polytopic integral protein of the inner membrane, is initially made in the cytoplasm as a soluble polypeptide (307 amino acids) lacking a cleavable targeting (signal) peptide. Earlier studies (Liu, X., Bell, A. W., Freeman, K. B., and Shore, G. C. (1988) J. Cell Biol. 107, 503-509) identified internal regions of the molecule that are critical for targeting and membrane insertion. Here, we demonstrate that the ability of uncoupling protein to insert into the inner membrane is abrogated when the molecule is fused behind the matrix-targeting signal of preornithine carbamyltransferase; the hybrid protein was imported across the inner membrane and deposited in the matrix where it was processed. In this context, however, the processed product remained in the matrix and was incapable of inserting into the inner membrane.
authors.affiliation: Department of Biochemistry, McGill University, Montreal, Canada.
authors.forename: X Q
authors.initials: XQ
authors.lastname: Liu
authors.forename: K B
authors.initials: KB
authors.lastname: Freeman
authors.forename: G C
authors.initials: GC
authors.lastname: Shore
mesh_terms: D000818:Animals; D001483:Base Sequence; D002352:Carrier Proteins; D004792:Enzyme Precursors / Q000235:genetics / Q000378:metabolism*; D007425:Intracellular Membranes / Q000378:metabolism*; D007473:Ion Channels; D008565:Membrane Proteins / Q000235:genetics / Q000378:metabolism*; D008929:Mitochondria, Heart / Q000378:metabolism* / Q000648:ultrastructure; D024101:Mitochondrial Proteins; D008969:Molecular Sequence Data; D009954:Ornithine Carbamoyltransferase / Q000235:genetics / Q000378:metabolism*; D021382:Protein Sorting Signals / Q000235:genetics / Q000378:metabolism*; D051381:Rats; D011994:Recombinant Proteins / Q000378:metabolism*; D014357:Trypsin / Q000494:pharmacology; D000071256:Uncoupling Protein 1; D015032:Zinc / Q000494:pharmacology
chemical_list: D002352:Carrier Proteins; D004792:Enzyme Precursors; D007473:Ion Channels; D008565:Membrane Proteins; D024101:Mitochondrial Proteins; D021382:Protein Sorting Signals; D011994:Recombinant Proteins; D000071256:Uncoupling Protein 1; C052289:preornithine carbamoyltransferase; D009954:Ornithine Carbamoyltransferase; D014357:Trypsin; D015032:Zinc